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Sei Whale - Balaenoptera borealis

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Sei whale

Sei Whale Statistics

Maximum length: 17.7m (58ft) males / 20m (66ft) females
Adult weight: 33 tonnes
Life span: 60 years
Sexual maturity: 8 - 11 years
10-5 - 12 months
Birth length: 4.5m (15ft)
Birth weight: 650 - 800kg (1300 - 1800lbs)
Dive duration: 20 mins
Distribution: all oceans, though waters from 8 - 25°C (46 - 77°F) are preferred
Current world population:
80 000 / pre-whaling 150 000

The sei (pronounced "say") whales are among the more elusive of the larger whales, not coming very close to land at any time and not forming large groups or "schools".

They are found like many whales in both Northern and Southern hemispheres following the best feeding at different times of year. Only the larger older individuals tend to go very far south, they are relatively rare in Antarctica. 

Sei whales favour temperate, deep offshore waters more so than other species of large whale, being rarely seen inshore. In the summer months, sei whales do not move as far towards the polar waters as other rorqual whales and do not usually enter icy water. This this way the large rorquals avoid competition for food resources, each having different feeding grounds, habitats and prey preferences. They skim feed on copepods (zooplankton) and other small prey, rather than lunging and gulping, like other rorquals. This largely explains the relative fineness of the baleen fringes and the shortness of the throat pleats in this species.

Sei whales have less and relatively shorter ventral throat grooves than blue, fin or minke whales, from 30 to 60, and reaching down to midway between the flippers and the navel. The largest baleen plates measure 75-80 cm and there are from 300 - 400 on each side of the jaw.

The back is often mottled with scars - probably from cookie-cutter shark bites.

Ecology and Behaviour

Sei whales are often seen in groups of two to five. They are fast swimmers, possibly the fastest of all cetaceans (whales and dolphins) reaching 50 kmh (31 mph) over short distances. When slow moving Sei whales surface, their blowholes and dorsal fin are often visible above the water at the same time. Feeding Sei whales tend to dive and surface in very predictable series, often remaining visible just below the surface between breaths.

Calving occurs in midwinter, in low latitude portions of the species' range.

Sei whale mother and calf - picture courtesy NOAA

Sei whale surface feeding, note the extended throat
due to the pleats allowing the skin to extend.
Photo- courtesy NOAA

Sei Whale, Swimming, Azores, Portugal
Sei Whale, Swimming, Azores, Portugal
Photographic Print

Sei Whale Comes Up for Air
Sei Whale Comes Up for Air
Giclee Print

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